The effects of lamotrigine on the pharmacokinetics of lithium

Aims The treatment of bipolar disorder often includes use of multiple drug therapies. Lithium is one of the most commonly used treatments, but has a n arrow therapeutic window. Lamotrigine, an established antiepileptic drug, i s emerging as a potentially important new therapy in the treatment of bipol ar disorder. The objective of this two-treatment crossover study was to det ermine whether lamotrigine affects lithium pharmacokinetics. Methods Twenty healthy adult men completed the study. Subjects took 2 g lit hium gluconate anhydrous every 12 h in the morning and evening for 5 days a nd in the morning of day 6, with or without 100 mg lamotrigine once daily i n the morning for 6 days. Blood and urine samples were collected on day 6 o f both treatments to characterize the pharmacokinetics of lithium using non compartmental methods. Results The geometric least-square mean ratio for renal clearance of lithiu m between the combination treatment and lithium alone treatment was 0.93 (9 5% confidence interval 0.85-1.02). Both treatments were well tolerated. Conclusions Lamotrigine does not cause significant change in the pharmacoki netics of lithium.